1. Field of the Invention
This invention relates to a fluid friction coupling comprising at least one coupling hub, a coupling housing rotatably supported on the coupling hub, and two sets of plates, one non-rotatably connected to the coupling hub and one non-rotatably connected to the coupling housing, the plates of the sets of plates being disposed in an alternating sequence with the plates of a first of the sets being held at predetermined spacings from one another while the plates of the other set are axially movable.
2. Description of Prior Art
With such fluid friction couplings such as they are known from West German Patent Specification No. 38 28 421 C1 and its British equivalent No. 2 222 232, spacing between the first set of plates is achieved by so-called spacer rings of a predetermined thickness. These spacer rings are slotted and as compared to the inner diameter of the coupling housing, they have a slightly increased outer diameter so that they rest against the inner housing wall in a prestressed condition. However, a disadvantage of this design is that automatic assembly of the plates is either not possible at all or causes great difficulties, which is the reason why the plates are still fitted by hand.
From U.S. Pat. No. 4,058,027, it is known to arrange a certain number of teeth on the plates in an angular position in order to achieve a spring-loaded return. However, for spacing the plates such an angular position is not suitable because the tolerances of the outer diameter and especially centering of the plates have to be very close to achieve uniform dimensions for the distances to be observed, whereas an articulated position, because of its spring-loaded return forces, does not permit such tolerances or only with considerable effort.
From West German Patent Specification No. 37 26 641 C1 and its British equivalent No. 2 207 983 it is known to provide one of the sets of plates with cam-like pressed-out regions which are aligned relative to each other in one direction of rotation and which increase the distance between the associated plates. However, it is the purpose of this design to provide the fluid friction coupling with different torque characteristics for the two directions of rotation; a predetermined distance between the plates cannot be achieved with such pressed-out regions.